Self-emulsifying drug delivery systems (SEDDSs) have
gained exposure for their ability to increase solubility and
bioavailability of poorly soluble drugs. SEDDSs are isotropic
mixtures of oils and surfactants, sometimes containing
cosolvents, and can be used for the design of formulations
in order to improve the oral absorption of highly lipophilic
compounds. SEDDSs emulsify spontaneously to produce
fine oil-in-water emulsions when introduced into an aqueous
phase under gentle agitation. SEDDS can be orally administered
in soft or hard gelatine capsules and form fine,
relatively stable oil-in-water emulsions upon aqueous dilution.
This article presents an overview of SEDDSs and their
applications.

In recent years, the formulation of poorly soluble compounds
presented interesting challenges for formulation
scientists in the pharmaceutical industry. Up to 40% of new
chemical entities discovered by the pharmaceutical industry
are poorly soluble or lipophilic compounds, which leads to
poor oral bioavailability, high intra- and inter-subject variability,
and lack of dose proportionality (1).

In the oral formulation of such compounds, a number of
attempts—such as decreasing particle size, use of wetting
agents, coprecipitation, and preparation of solid dispersions—
have been made to modify the dissolution profile and
thereby improve the absorption rate. Recently, much attention
has focused on lipid-based formulations to improve the
bioavailability of poorly water soluble drugs. Among many
such delivery options, like incorporation of drugs in oils (2),
surfactant dispersion (3), emulsions (4) and liposomes (5),
one of the most popular approaches are the self-emulsifying
drug delivery systems (SEDDSs).

SEDDSs are mixtures of oils and surfactants, ideally isotropic
and sometimes containing cosolvents, which emulsify
spontaneously to produce fine oil-in-water emulsions when
introduced into an aqueous phase under gentle agitation.
Self-emulsifying formulations spread readily in the gastrointestinal
(GI) tract, and the digestive motility of the stomach
and the intestine provide the agitation necessary for selfemulsification.
These systems advantageously present the drug in dissolved form and the small droplet size provides
a large interfacial area for the drug absorption (6). SEDDSs
typically produce emulsions with a droplet size between
100–300 nm while self-microemulsifying drug delivery systems
(SMEDDSs) form transparent microemulsions with a
droplet size of less than 50 nm. When compared with emulsions,
which are sensitive and metastable dispersed forms,
SEDDSs are physically stable formulations that are easy to
manufacture. Thus, for lipophilic drug compounds that exhibit
dissolution rate-limited absorption, these systems may
offer an improvement in the rate and extent of absorption
and result in more reproducible blood-time profiles (7).